Immobilization of animal rennet.

Rennet was immobilized on porous glass beads (50-100 mesh) using diazotization [Paquot et al., DSA 38, 5851], TiCl4 [Barker et al., Process Biochemistry (1971) 5, 11], glutaraldehyde [Stanley & Olson, Journal of Food Science (1974) 39, 660] or glutaraldehyde followed by reduction of aldehyde groups by NaBH4 [Cheryan et al., DSA 38, 6728]. Residual enzyme activity was low using all 4 methods, being highest using TiCl4 (24.4%). After 13 days storage, loss of enzyme activity using diazotization and TiCl4 was resp. 82 and 58%. Activity of rennet immobilized using TiCl4 decreased with time during the passage of milk through the column, this being due to release of enzyme rather than denaturation. Ca2+ ions were responsible for the release; loss of enzyme activity during four 15-min passages of whey, casein solution (pH 7) and casein solution + EDTA was resp. 87, 57 and 4.5%. Precoating the glass beads with serum albumin resulted in significant increases in residual activity of rennet, particularly when immobilized using glutaraldehyde/NaBH4. This improvement diminished on storage.